1. Field of the Invention
The present invention relates to ink for inkjet recording containing dye and water, an inkjet recording method, an inkjet recording head and a manufacturing method therefor, and an inkjet printer. In particular, the present invention relates to ink for inkjet recording and an inkjet recording head that can greatly suppress the kogation phenomenon peculiar to thermal inkjet printers.
2. Description of the Related Art
Recently, the need for color hard copies has increased significantly in the field of image processing. Various methods for producing color hard copies have been developed. Examples thereof include dye-sublimation recording, thermal wax transfer recording, inkjet recording, electrophotographic recording, and thermally processed silver recording.
In inkjet printing, ink droplets are ejected from aligned nozzles of an inkjet recording head of an inkjet printer onto a recording medium such as paper. The ejected droplets form points called “dots” to create characters and images. The advantages of inkjet printing over other printing methods are its low cost, high quality, and ability to easily produce color images. Ink used in inkjet printing is prepared by dissolving or dispersing a water-soluble dye or pigment into a solvent containing water and water-soluble organic solvent. An additive such as a surfactant may be added if necessary.
Inkjet printing can be classified according to the method of ejecting ink droplets: piezoelectric methods in which piezoelectric devices are used to eject ink and thermal methods in which heater devices are used to eject ink.
According to the thermal printing method, ink contained in a reservoir of an inkjet recording head is locally heated by a heater device to generate bubbles and to thereby discharge ink droplets from the reservoir through orifices, such as nozzles, onto a recording medium. A thermal-type printer thus has an inkjet recording head that includes a heater device for heating ink, the heater device being installed inside the reservoir, and a driving circuit for driving the heater device, such as a logic integrated circuit.
However, when conventional ink for use in inkjet recording is used in the thermal inkjet printer, foreign matter such as impurities, e.g., metal ions introduced during synthesis of the dye, or thermal decomposition products deposit on the surface of the heater device as the inkjet printer is used. This phenomenon is called “kogation”. Kogation causes local heating of ink to become insufficient, inhibits generation of bubbles, decreases the discharge rate of the ink, and adversely affect discharge of ink droplets.
One proposed technique for preventing kogation is to remove from the dye impurities such as metal ions introduced during synthesis of the dye. However, thermal decomposition of the dye in the ink is inevitable. Even when impurities such as metal ions are removed by purifying the ink, deposition of the decomposition products of the dye onto the heater device cannot be prevented. Thus, kogation cannot be completely prevented according to this technique.
According to the conventional technology, kogation cannot be completely prevented as long as ink containing dye, water, and an organic solvent is used in the inkjet recording, as described above.